The classic portraits we usually see of polar bears are of the majestic white creatures against a stunning backdrop of Arctic ice. But these heartbreaking photographs of the polar bears on the shores of Canada’s Hudson Bay tell a very different story. The National Wildlife Federation hopes that newly released images will spark a much-needed conversation about climate change.

“Some of (the polar bears) are much more visibly thin than they used to be,” says the National Wildlife Federation’s Senior Scientist Dr. Douglas B.Inkley. “We’re seeing their backbones, their shoulder blades, their hips. And because they’re much lighter in weight they are less able to successfully reproduce.”

Every fall, on the shores of Manitoba’s Hudson Bay, hundreds of polar bears gather to wait for ice to freeze over the water, which allows them to hunt for their natural food source, seals. While they wait, the polar bears 'daybed' in permafrost, as seen in the images above. The only problem? Warmer temperatures and longer summers mean the bears have spent a longer time fasting, which over 30 years has taken its toll. Inkley says that female polar bears in the population are now averaging 90 pounds lighter, leading to plunging birth rates and survival rates for cubs.

So why is the ice taking longer to freeze? For Inkley, the answer is simple:

“This is climate change at work," he says. “We no longer need to argue in society about whether or not climate change is real and whether or not it's being caused by our carbon emissions … We are responsible for this. There’s no question about it.”

In 25 years, the polar bear population at Hudson Bay has declined dramatically. Scientists predict that the population will continue to shrink to what Inkley calls a tipping point, experience a population crash and die out. And unfortunately, there’s not much that can be done for the bears in western Hudson Bay. But they have been of particular interest to scientists because they are at the southernmost extent of the polar bear’s range, and could give insight into how a warming climate may affect other populations of the animals in the future.

“People regard the polar bears in Hudson Bay as the canary in the coal mine,“ says Inkley. “That population is most likely to feel any potential effects of climate change before other polar bear populations.“